Put snow into a pot. Take a glass plate and wash it. Sprinkle a spoon of salt into the pot. Be careful not to throw any salt on the plate. Wait for a while and look at the pot. The pot is frozen onto the plate.
The temperature of the snow has gone down. The salt destroy the crystals of snow and makes them melt. Lots of heat is needed to melt the snow. It is taken from everything around. That´s why the temperature drops.